Importance: Oral corticosteroids (OCSs) are increasingly used during pregnancy for various conditions due to their immunosuppressive and anti-inflammatory properties. However, OCSs may induce insulin resistance, potentially contributing to gestational diabetes, and limited studies have examined this association.
Objective: To assess the risk of gestational diabetes associated with OCS use during pregnancy.
Design, setting, and participants: This nationwide, population-based cohort study included pregnancies resulting in live births in Korea from 2010 through 2021. A sequential landmark analysis was conducted, with OCS exposure assessed in 3-week intervals between 1 and 27 weeks' gestation. Data were analyzed from June 26, 2024, to September 19, 2025.
Exposure: Pregnancies among women who were exposed to OCSs were compared with pregnancies among women who were not exposed to OCSs within each 3-week interval and in pooled analyses.
Main outcomes and measures: Gestational diabetes was assessed from 20 weeks plus 1 day of gestation until delivery using a previously validated algorithm. Propensity score-based overlap weighting was applied to adjust for comorbidities, medication use, and health care utilization. Risk ratios (RRs) and 95% CIs were estimated using bootstrapping with 200 replications. Subgroup analyses by age, indication, duration of action, dose, timing, and duration of exposures were performed.
Results: Among 3 848 270 pregnancies, 1 325 940 were eligible for analysis, of which 79 710 (6.0%) were exposed to OCSs between 1 and 27 weeks' gestation. OCS exposure was not associated with an increased risk of gestational diabetes in most intervals, except between 4 and 6 weeks' gestation (weighted RR, 1.10; 95% CI, 1.03-1.17). In the pooled analysis, gestational diabetes occurred in 9.50% (95% CI, 9.26%-9.74%) of pregnancies among women in the exposed group vs 7.36% (95% CI, 7.31%-7.43%) of pregnancies among those in the unexposed group (weighted RR, 1.01; 95% CI, 0.99-1.03). Subgroup analyses showed no significant effect modification by maternal age, indication, duration of action, dosage, timing, or duration of exposure.
Conclusions and relevance: In this cohort study, OCS exposure during pregnancy was not associated with an increased risk of gestational diabetes, except for a modest increase in risk among women exposed to OCSs between 4 and 6 weeks' gestation, supporting the use of OCSs when clinically indicated.